If you work a lot with forms which also should be usable in Adobe Reader, you have to apply the "Additional Features" (Usage Rights in Adobe Reader) with Acrobat.
Too bad that you later cannot see which form already has been Reader-enabled.
In Acrobat you only can try to apply the Usage Rights again, which then returns an error message.
That's annoying, as you have to navigate through several sub menus to call the specific menu item.

Obviously you could install Adobe Reader parallel to Acrobat, where you easily can see if the form is saveable.
But, Adobe strict advises againt a parallel installation of both application on the same system, and who else better knows why.

So, for this purpose I wrote a small folder level script, which adds a new menu item in the "File" menu and under "Tools" > "Add-on Tools".
With it you easily can check you file for Usage Rights and also apply them if neccessary.